1. Field of the Invention
The present invention relates to insulated wire and cable made of such insulated wire and insulation suitable for use in vessels and aircrafts.
2. Description of Related Art
One example of prior art is disclosed in the specification of U.S. Pat. No. 4,521,485. The specification discloses an insulated electrical article which comprises a conductor, a melt-shaped inner insulating layer comprising a first organic polymer component and a melt-shaped outer insulating layer contacting said inner layer and comprising a second organic polymer component and which is useful for aircraft wire and cable. The inner insulating layer comprises a cross-linked fluorocarbon polymer or fluorine-containing polymer containing 10% by weight or more of fluorine fluorocarbon polymer being ethylene/tetrafluoroethylene copolymer, ethylene/chlorotrifluoroethylene copolymer, or vinylidene fluoride polymer. The outer insulating layer comprises a substantially linear aromatic polymer having a glass transition temperature of at least 100.degree. C., the aromatic polymer being polyketone, polyether ether ketone, polyether ketone, polyether sulfone, polyether ketone/sulfone copolymer or polyether imide. The specification of U.S. Pat. No. 4,678,709 discloses another example of prior art insulated article which comprises a cross-linked olefin polymer such as polyethylene, methyl, ethyl acrylate, and vinyl acetate as the first organic polymer of the inner insulating layer.
According to the second example of prior art, the aromatic polymer used in the outer insulating layer must be crystallized in order to improve its chemical resistance. For such crystallization, cooling which follows extrusion of the outer layer at 240.degree. C..about.440.degree. C. must be carried out gradually rather than rapidly. Alternatively, additional heating at 160.degree. C..about.300.degree. C. must be conducted following extrusion. Such step entails a disadvantage that the cross-linked polyolefin polymer in the inner insulating layer becomes melted and decomposed by the heat for crystallization, causing deformation or foaming in the inner layer. If the outer layer is cooled with air or water immediately after extrusion thereof, melting or decomposition of the inner layer may be avoided but the outer layer remains uncrystallized. This leads to inferior chemical resistance, and when contacted with particular chemicals, the outer uncrystallized insulating layer would become cracked or melted. Use of a non-crystalline polymer such as polyarylate as the aromatic polymer of the outer insulating layer also provides unsatisfactory chemical resistance.
Further, the prior art insulation articles do not have sufficient dielectric breakdown characteristics under bending. Insulated articles having excellent flexibility, reduced ratio of defects such as pin holes, and excellent electric properties are therefore in demand.